1. Field of the Invention
The present invention relates to an image forming apparatus, such as a copying machine, a printer, a facsimile machine, and a complex machine having functions of those, which adopts an electrophotographic method.
2. Description of the Related Art
An image forming apparatus, such as a copying machine, a printer, a facsimile machine, and a complex machine having functions of those, adopting an electrophotographic method includes an image bearing member, a charging device which is adapted to evenly charge a surface of the image bearing member, an exposure device which is adapted to form an electrostatic latent image on the image bearing member, a developing device which is adapted to develop the electrostatic latent image formed on the image bearing member to be a toner image, and a transferring device which is adapted to transfer the toner image formed on the image bearing member to a sheet. Further, there may be further provided a cleaning device which is adapted to remove toners, which reside on the image bearing member after the toner image formed on the image bearing member is transferred to the sheet, from the image bearing member.
In such image forming apparatus, there has been a known image forming apparatus using an endless belt wound around a plurality of rollers. For example, such image forming apparatus includes an image forming apparatus which has an intermediate image bearing member including a belt (intermediate transferring belt) and adapted to primarily receive a toner image formed on the image bearing member by the electrophotographic method and thereafter secondarily transfer the toner image to a transfer member, and an image forming apparatus which has a transfer member conveying member including a belt (transfer member conveying belt) and adapted to directly transfer the toner image bore by the image bearing member, and an image forming apparatus which has an image bearing member including a belt (photoconductive belt) and adapted to bear a toner image formed by the electrophotographic method.
For example, the image forming apparatus using the intermediate transferring belt includes a tandem color image forming apparatus having a color printing function of forming a color image by superimposing toners of a plurality of colors, such as yellow (Y), magenta (M), cyan (C), and black (K) onto the intermediate transferring belt. In such color image forming apparatus, developing devices corresponding to respective colors are arranged along the intermediate transferring belt to superimpose toners of a plurality of colors. Further, the intermediate transferring belt is wound around a plurality of rollers, and the plurality of rollers are classified into a driving roller adapted to drive the intermediate transferring belt and a driven roller driven by the driving roller via the movement of the intermediate transferring belt.
In accordance with the driving of the driving roller, toner images of four colors, e.g. Y, M, C, K, formed by respective photoconductive drums of the developing devices are sequentially transferred (primarily transferred) to the intermediate transferring belt so that the toner images are superimposed one after another. Then, the color image formed on the intermediate transferring belt is transferred (secondarily transferred) to a transfer member such as a sheet by a secondary transferring roller which is provided so as to face the intermediate transferring belt. However, when a metal roller made of aluminum or the like is used as a driven roller in the tandem image forming apparatus, the intermediate transferring belt and the metal roller come into friction, so that a surface (back surface) of the intermediate transferring belt in contact with the metal roller, and a surface of the metal roller get damaged. Thus, if the image forming is performed for a long time, such damage becomes noticeable, so that it causes uneven thickness of the intermediate transferring belt to occur. A high-quality image cannot be obtained by such intermediate transferring belt having an uneven thickness even if the secondary transfer is performed by applying a predetermined bias to the intermediate transferring belt.
As an example of an image forming apparatus using a belt wound around a plurality of rollers to reduce such occurrence of uneven thickness of the belt, there has been a known image forming apparatus in which a hollow pipe made of aluminum which has a surface hardness of 500 HV or greater and a surface roughness Rz of 2 μm or less is used as a roller around which a belt (transfer member conveying belt) is wound (refer to Japanese Patent Unexamined Publication No. 2005-43593: hereinafter, referred to as a patent document 1).
The above-described patent document 1 discloses that when the hollow pipe is used as a roller, a surface nature of the roller can be maintained regardless of the number of times of use and a use environment, so that damage to the belt can be reduced.
However, occurrence of the uneven thickness cannot be actually reduced by the configuration of the patent document 1, and generation of such damage on the belt may become earlier. Therefore, this image forming apparatus cannot form a high-quality image.